Fragile X syndrome (FXS) is the leading single-gene disorder associated with a diagnosis of autism. The proposed research will compare language prosody of boys with autism spectrum disorder (ASD) only (ASD-O), FXS with ASD (FXS-ASD), FXS only (FXS-O), and typical development (TD) to identify precise autism phenotypes that could be linked with the Fragile X Mental Retardation-1 gene (FMR1). The specific aims are to identify profiles of language prosody that overlap in autism and FXS or are specific to autism, to determine concordance between rater judgments and objective quantitative indices of prosody, and to determine whether social cognition accounts for anticipated group differences in prosody. 40 boys with ASD-O, 40 boys with FXS- ASD, 40 boys with FXS-O, and 50 TD boys (25 with similar language age [TD-LA] and 25 with similar chronological age [TD-CA]) will be assessed once over a 2-year period. The boys with ASD-O, FXS-ASD, FXS-O, and TD-CA will be between 8 and 12 years of age and the TD-LA boys will be between 3 and 6 years of age. The boys with ASD, FXS, and TD-LA will be functioning at a language level between 3 and 6 years of age. The boys'language in imitated sentences and conversational speech will be examined for prosody using both acoustic measures (F0 variation, utterance final F0 drop, actual articulation rate, and the pairwise variability index [PVI]) and perceptual measures (listener judgments of phrasing, rate, and stress from The Prosody-Voice Screening Profile [PVSP]). In addition, a direct magnitude estimation (DME) study will be used to assess perceived peculiarity of speech. Relationships between judgments of prosodic peculiarity and specific aspects of prosody, as well as the relationship between social cognition (theory of mind) and prosody, will be examined. Hierarchical linear modeling (HLM) and multiple linear regression will be used to address the research questions. Atypical prosody, a core feature of the language of verbal individuals with autism, can affect perceived communicative competence in significant ways. As well as furthering our understanding of the association between autism and FMR1, determining the differences and overlap in prosodic profiles of boys with FXS and ASD using both rater judgments and objective measures has important clinical implications. PUBLIC HEALTH RELEVANCE: Atypical prosody, a core feature of language in autism, can compromise communicative competence in daily interactions. Fragile X syndrome (FXS) is the leading single-gene disorder associated with a diagnosis of autism. Determining the differences and overlap in prosodic profiles of boys with FXS and autism has highly significant implications for determining treatment protocols.